Orthotic products are commonly made with hard, moldable substrates such as malleable plastic materials. Different techniques such as offset printing can be used to print a decorative graphic, design, or image on surfaces of orthotic substrates. However, offset printing is time consuming and labor intensive. The ink mixture must be pre-tested to determine if the ink color, when transferred from a plate to a rubber blanket to the substrate surface, is true to the colors of the original design. If not, the ink must be remixed and retested to achieve the desired shade. Also, individual ink colors are printed separately. A decorative design having multiple ink colors must be re-printed with each color layered upon the other. As a result, offset printing offers a limited number of printed designs that are not easily customized due to time and labor constraints. Additionally, with this printing method, the ink adhesion to the orthotic substrate surface is poor, resulting in a printed design having inadequate scratch resistance.
Digital printing systems, e.g., laser printers, inkjet printers, digital web presses, etc., are faster than offset printing. Image applications can be used to create or customize a computer image file before it is printed on an orthotic substrate surface. Digital printers use the guidance of computer software to mix cyan, magenta, yellow, and black inks (“CMYK inks”) to print decorative designs that accurately match the colors of the computer image file. This printing method can rapidly print an endless number of colorful graphics, designs, and/or images to meet specific color or size requirements on paper, textiles, and other surfaces. However, digital printers merely deposit a thin layer of CMYK inks on the orthotic substrate surface. The printed design can easily be scratched, rubbed, and removed from the orthotic substrate surface unless the CMYK inks are additionally adhered to the substrate using a secondary heat or curing process, which requires additional time and expense. Cracking, fading, and peeling are also common problems with digitally printed designs on moldable orthotic substrates.
Digital dye-sublimation printing can be used to quickly print vibrant designs that are durable and permanent on polyester substrates, i.e., polyester textiles or non-polyester substrates that have been pre-coated with a polyester surface. A combination of heat, pressure, and time causes the dye-sublimation CMYK inks to permeate the polyester substrate creating a scratch-resistant design that does not crack, fade, or peel. However, the heat and pressure melt and compress a moldable orthotic substrate making it unusable for orthotic product manufacturing.
To explain further, digital dye-sublimation printing comprises a two-part process. First, a digital printing system using special CMYK inks that sublimate, i.e., transition from a solid to a gas state when heat and pressure are applied for a period of time, to print a computer image file on a digital transfer paper substrate. The digital transfer paper substrate can be single sheets of paper or paper rolls, depending on the type of digital printing system that is used and the size and number of decorative designs to be printed. Second, the decorative printed design is transferred from the digital transfer paper substrate to a polyester substrate using a dye-sublimation printer, e.g., a flatbed heat press (for single sheets of paper) or an oil-heated roller calendar heat press (for large paper rolls). The digital transfer paper substrate is placed print side down on the polyester substrate, forming a duo-layered substrate. Pressure (approximately 120 psi) and heat (approximately 380-420 degrees Fahrenheit) are then applied to the duo-layered substrate using the dye-sublimation printer to sublimate and transfer the dye-sublimation CMYK inks from the digital transfer paper substrate to the polyester substrate. The heat opens the pores of the polyester substrate, and the applied pressure forces the dye gases to enter the open pores. When transfer of the dye-sublimation CMYK inks is competed (typically 30-90 seconds), the digital transfer paper substrate is removed from the polyester substrate. The pores of the polyester substrate close as it cools, and the dye-sublimation CMYK ink gases revert to a solid state, becoming part of the substrate. No drying time or post-treatment of the polyester substrate is required. One important advantage of dye-sublimation printing is that the results are permanent. Dye-sublimation CMYK inks penetrate the polyester substrate creating a durable, scratch-resistant design that does not crack, fade, or peel. In addition, the vibrant colors of the print design on the polyester substrate are true to the original computer image file.
Nevertheless, dye-sublimation printing is unsuitable for printing decorative designs on moldable orthotic substrates due to the dye-sublimation requirements. Orthotic substrates are typically malleable sheets of plastic material, e.g., polypropylene, having a thickness of ⅛-¼ inches. Heating a sheet of polypropylene to 380-420 degrees Fahrenheit for 30-90 seconds melts the plastic, and the added 120 psi required for ink transfer thins and warps the shape of the polypropylene sheet. Another important problem with dye-sublimation printing is the polyester substrate requirement. Polyester sheets that are ⅛-¼ inches thick are brittle and unmalleable, which makes them unsuitable for use as orthotic substrates.